HEQ5 standard ratio 9:47 belt mod.

[1parsec]

I have looked with interest at the various belt mods for the HEQ5 to help improve tracking performance and

reduce that rather disturbing 'rattling bag of bolts' sound during slew acceleration and deceleration.

But I didn't want to be reliant on a pc to allow for the non-standard gear ratio as I like to keep things a simple

as possible for taking my gear mobile. So I made a few drawings of the drive train of the HEQ5 to see

if a standard ratio belt system would be possible. The cad drawing shows a few options possible with the different

standard belt lengths available. A couple of options use an idler which would help make tensioning easier.

The 9 tooth pully is the tricky part !! Standard pulleys are just too small to allow the bore to be opened out

to the 5mm motor shaft diameter, so the only option is a custom machined pulley with an extended rear

mounting.

I have had a bit of time over the last few days and machined a couple of the 9T pulleys. I was initially a bit

concerned that the tiny radius of the pulley would be just too tight to allow the belt to follow around but the

2.5 pitch 6mm wide synchroflex belts do it with out any problem.

The teeth on the pulley are not machined fully out of the end but stop short. I'm hoping this will mean the

belt will say in place with out the need of a full flange on the face of the pulley.

As the pulley stands off the end of the motor shaft by 10.5mm further than the original gear,a new aluminium

cover is planned to accommodate the extra bit and pieces inside the gearbox housing.

I'll update this thread as more ideas, drawings & parts are made.

Dave.

[malc-c]

Nice workmanship

There is a need for a belt drive conversion that maintains the default ratio for use with the handset as not everyone wants to use a PC / Laptop, and your solution seems to overcome the main area of weakness, that of boring out the 9mm pulley. I'm sure if you get this right you'll receive lots of inquiries for a kit.

[JamesF]

That does look very neat

James

[1parsec]

Thanks Malc and James. It's going to an interesting project,

I'm working on the 47T pulley next and I hope to have some time to do those at the end of the week.

The pulleys will be 10.5mm above the surface of the side casting so it's going to need a new side cover which

should be possible to machine from 12mm aluminium plate.

My first idea shows the top and bottom of the pulley pockets.

Dave.

[Cath]

I guess their is next to no backlash with toothed pulley drives if the belt is nice and tight and the belt fits the teeth without movement?

[JamesF]

I'm just trying to work out if I can make these pulleys on a lathe without access to a milling machine

Given a suitable divider I reckon it might be possible, if I mount the divider and a chuck in the place of the toolpost with the cutting tool in the main chuck, then use the cross slide and top slide to advance the workpiece.

James

[malc-c]

Thanks Malc and James. It's going to an interesting project,

I'm working on the 47T pulley next and I hope to have some time to do those at the end of the week.

The pulleys will be 10.5mm above the surface of the side casting so it's going to need a new side cover which

should be possible to machine from 12mm aluminium plate.

My first idea shows the top and bottom of the pulley pockets.

Dave.

Wow.... I take it you have your own CNC machine ?

The alternative is to laser cut a spacer from perspex or suitable material. I would be interested to hear what sort of retail costs you could retail these kits for as I'm sure if you could sell them cheaper than the 120 euros advertised for the current kits there would be a lot of interest. Now only if someone could come up with a direct belt drive mod to remove the backlash in the worm gear......

[1parsec]

I'm just trying to work out if I can make these pulleys on a lathe without access to a milling machine

Given a suitable divider I reckon it might be possible, if I mount the divider and a chuck in the place of the toolpost with the cutting tool in the main chuck, then use the cross slide and top slide to advance the workpiece.

James

James it should be possible to do the pulley on a lathe with an indexer as you've described.

You'll also need a method of positioning the indexer center line above and below the lathe spindle centre line to allow you

to machine the trapezoidal tooth form of 20 degrees each side of the tooth.

The main difficulty you'll have is using a 1.0mm diameter cutter and not breaking it . Very high spindle speeds is good -

The width at the root of each of the pulley teeth is about 1.0mm for a t2.5 belt.

The other method is broaching, also possible on a lathe.

Dave.

[1parsec]

Wow.... I take it you have your own CNC machine ?

The alternative is to laser cut a spacer from perspex or suitable material. I would be interested to hear what sort of retail costs you could retail these kits for as I'm sure if you could sell them cheaper than the 120 euros advertised for the current kits there would be a lot of interest. Now only if someone could come up with a direct belt drive mod to remove the backlash in the worm gear......

Hi Malcolm, Yes I have a cnc mill and cnc lathe at my works which can be put to good use some times

120 Euros does seem expensive for 4 pulleys and 2 belts and I'm sure it would be possible to get a kit together for a good bit less than that.

I've seen the spacers you supplied with your kits . I'll look in to that method also, but I'm not sure if it will be possible to get it laser cut

thick enough to make the cover clear the pulleys...

An aluminium machined cover would be an expensive part- but it would look very nice

Lots of things still to do.

Dave.

[Freff]

I would love to install a forth axis on my CNC machine at home. It would make making these pulleys simple.

[JamesF]

I find myself wondering now if you have created a completely unique item. The smallest T2.5 pulleys I can find online have ten teeth

James

[JamesF]

I've seen the spacers you supplied with your kits . I'll look in to that method also, but I'm not sure if it will be possible to get it laser cut

thick enough to make the cover clear the pulleys...

Cut it half the thickness and use two, perhaps?

James

[Fred_76]

Hi!

Nice pulleys !

As long as your are competitive with the kits sold by Tavcso or Telescope Service Austria (about 120€ for the two sets for DEC and RA plus the spacer) I wish you a lot of success.

Fred

[1parsec]

Thanks for the replies Malcolm, James and Fred.

A spacer-gasket for the cover will probably be the way to go but I'd like to see what a full machined aluminium cover would look like

Here's the 47T pulley completed today.

Next step is to get the mount set up and take some track logs with the standard gear train as they are as set from the SW factory.

This might be possible this weekend looking at the weather forecast- surely I wont be that lucky

As soon as I've got good data on the tracking performance I'll fit the pulleys and belts and take further track logs.

Dave.

[JamesF]

Those do look very nice.

I wonder why they chose such an awkward ratio when the mount was designed? I assume there must be a good reason for it. Perhaps so the same teeth in the gears rarely meet?

James

[Fred_76]

This ratio is a pure non sense. A 9 teeth gear on a 30+ transfer gear interfere a lot and the teeth shall be rectified. This is quite a costly and difficult operation to do it properly. That is why the PE of the HEQ5 is so erratic in the gear mesh period.

One should always avoid gears with less than 13 teeth...

[Fred_76]

@1parsec :

I see on your pictures that you've installed two set screws on the 9T pulley. Do you believe this is really necessary ?

[1parsec]

I see on your pictures that you've installed two set screws on the 9T pulley. Do you believe this is really necessary ?

I'll always try to fit 2 set screws to any size pulley. It makes the pulley contact more secure on the motor shaft.

The extra time to drill and tap 1 extra hole is minimal and well worthwhile.

Dave.

[JamesF]

This ratio is a pure non sense. A 9 teeth gear on a 30+ transfer gear interfere a lot and the teeth shall be rectified. This is quite a costly and difficult operation to do it properly. That is why the PE of the HEQ5 is so erratic in the gear mesh period.

Then why would an engineer have designed it in such a way?

James

[1parsec]

Then why would an engineer have designed it in such a way?

James

Design compromise. The engineers probably wanted to use a larger pinion gear but the sales team wanted 800x maximum slew speed

The design for 800x slew speed means the motor pinion needed is 9 teeth with the motors they use.

( Better motors or higher quality gear train would push the price too high?)

If they'd used 13T or larger pinion gear the maximum slew speed is reduced to 500X or there abouts but the gear mesh tooth to tooth would be smoother.

A belt drive allows multiple teeth to be in contact and tooth to tooth errors are averaged / reduced.

Dave.

[1parsec]

Ah, must remember to put brain in gear. Of course a larger pinion would increase the slew speed

[1parsec]

Before going ahead to fit the pulleys and belts I took some tracking logs last night for a before & after comparison and dropped them in to PecPrep .

The mount is as standard, not tweaked or changed at all.

First look, there doesn't seem to be a regular periodic error but appears a bit chaotic

Pecprep is an amazing tool for analysing and the frequency specturm shows 2 main errors. The worm error and also

an even bigger peak for the transfer gear which I wasn't expecting. Has any one seen that before and know the cause ?

With the belt mod, the transfer gear is out of the train so I'm not worried about it but it would be good to know why it was so bad.

Dave.

[1parsec]

I'm on with the fitting of the pulleys. The RA first.

I made a small extactor to remove the motor pinion gear with out damaging it. It pulled off a treat

I'm hoping to get a track log with the belt drive tonight if I can get it all together.

Dave.

[1parsec]

Here's the 9T pulley fitted to the motor shaft.

I check the run out on the end of the pulley and it was less than 0.02mm

Dave.

[1parsec]

Both 9T and 47T pulleys fitted.

The side of motor needed trimming by about 1mm to move closer to the 47T pulley to allow the belt to fit.

I'm going to try a longer belt with an idler / tensioner running on a pin fitted in the transfer gear position which

will allow easier tensioning adjustment.

But before that a track looking at the clear sky..

A quick video of the belt mod fitted to RA.

Dave